The present invention relates to a charged particle beam irradiation apparatus such as a scanning electron microscope, an X-ray micro-analyzer, and so on, and an irradiation method using the irradiation apparatus, and especially relates to an improved charged particle beam irradiation apparatus and an irradiation method using the irradiation apparatus, in which a display unit is used to designate a position on an image of a target area in a specimen, the target area being observed or analyzed by irradiation with a charged particle beam.
Scanning electron microscope, an X-ray micro-analyzer, etc., are known charged particle irradiation apparatuses. In a scanning electron microscope, a specimen is observed or inspected by using a magnified image of the specimen, which is formed by detecting secondary electrons or reflected electrons generated from the specimen irradiated with an electron beam. On the other hand, in an X-ray micro-analyzer, a specimen is examined by analyzing an X-ray emitted from the specimen irradiated with an electron beam. When a target area in a specimen, to be observed or analyzed by irradiation with a charged particle beam, is designated, a larger view of the specimen is displayed on an image display unit such as a CRT, an observation monitor, etc., by decreasing the magnification of the charged particle beam irradiation apparatus, and an image of the designated area in the specimen is moved near the central point on a viewscreen of the image display unit. Afterward, by gradually increasing the magnification, a view with the required magnification is obtained. However, since the magnified size of an inspected region in the specimen is smaller than the image resolution of the image display unit at the low magnification, the fine structure of the specimen is invisible, and it is difficult to find a point in the specimen to observe. Thus, an operator searches an inspected point in the displayed view by alternately repeating the specimen movement performed by operating a specimen fine movement device, and increasing the signification; or by moving the specimen fine movement device while observing the specimen with the magnification kept somewhat high.
Recently, there has been a stronger tendency for the inspection of a semiconductor memory to be performed with a scanning electron microscope in the fabrication processing of semiconductor memories. Usually in a semiconductor memory, a large number of cells with the same structure are arranged in an orderly latticework. Therefore, it is very difficult to quickly find a target cell on the viewscreen of a scanning electron microscope. When an operator searches a target cell in a specimen such as the above-mentioned semiconductor memory, the operator needs to memorize the row and column coordinates of the target cell in the specimen, and then find the target cell by counting the number of rows and columns in the latticework pattern by maintaining a somewhat high magnification such that the operator can discriminate each cell, and by gradually moving the specimen with a specimen fine movement device.
In a new type scanning electron microscope such that disclosed in Japanese Patent Application Laid-Open Hei 4-27908, if an operator designates any target position which s/he wants to observe in an image displayed on a viewscreen of an image display unit, a specimen fine movement device is automatically controlled by a motor so that the designated position is set at the central position of the viewscreen of the image display device. However, the operator needs to find the target position on the image of the specimen, which gives a comparatively heavy load on the operator.
The following method using the above new type scanning electron microscope has been devised as a measure to reduce the load of the operator having to designate a target position on the viewscreen of the image display unit. That is, in the new type scanning electron microscope, the first and second windows for displaying two images of the specimen, which are processed with high and low magnification respectively, are provided in the image display unit of this scanning electron microscope. Moreover, an area cursor is also displayed in the first window for the image processed with low magnification. Furthermore, it is possible to display the region inside the area cursor in the second window for high magnification. Thus, if the operator intends to observe a target cell at a position far from a terminal side position in a semiconductor memory, from which the searching of the target cell is started, the image of the specimen is displayed in the first window with a sufficiently decreased magnification, and the position where the target cell is located is enclosed in the area cursor. Further, the region enclosed in the area cursor is displayed in the second window with an appropriately increased magnification.
However, in the above-mentioned conventional scanning electron microscopes, if an operator searches for a position apart from one at a terminal side of a specimen by tens of columns or rows in an image formed with the magnification kept high to a extent such that the operator can discriminate the structure of a cell to be analyzed, the operator has to count the number of columns or rows from the terminal side to the position of the target cell. Also, in the scanning electron microscope with the ability to display images of the specimen at different magnifications, since an image of the target cell structure to be analyzed is too small on a viewscreen displaying a low-magnification image, it is difficult to count the number of columns or rows of cells. Even if the scanning electron microscope has the ability to automatically move the designated position of an image of the target cell in the specimen displayed on the viewscreen to the central position of the viewscreen, it is still necessary to count cells in the specimen while maintaining the magnification as high as necessary. Further, if the target cell is at a position far from a terminal side of the specimen by tens or hundreds of columns or rows of cells, since the target cell cannot be found with single specimen-movement operation, it is necessary to repeat the specimen-movement operation to find the target cell. The parallel execution of both the counting of the number of columns or rows and the repeating of the specimen-movement operation is likely to cause an error in the operator""s counting of the number of columns or rows, for example, missing some columns or rows.
The present invention has been achieved in consideration of the above mentioned problems. For example, it is effective for solving the problems of both providing a means to reduce the effort of finding a target position in a specimen, and of counting the number of columns or rows in an orderly latticework pattern of cells in the specimen with the same structure. Thus, an object of the present invention is to provide a charged particle beam irradiation apparatus wherein the searching for target cells to be observed in a specimen by operating a viewscreen with images of cells of the specimen can be easily carried out by an operator even if there are many cells arranged in the specimen in an orderly latticework.
The above object of the present invention is attained by providing a charged particle beam irradiation apparatus in which if an operator attaches a marker to a position to be observed on the image of a specimen, the marker also is moved along with the position of the specimen image as though the marker were attached to the position of the actual specimen when the image of the specimen is moved.
The present invention provides a charged particle beam irradiation apparatus comprising:
a specimen stage for holding a specimen;
a specimen stage drive unit for moving the specimen stage, a detector for detecting the amount of displacement of the moved specimen stage;
a charged particle beam optical unit for irradiating the specimen with a charged particle beam;
an image display unit for displaying an image of the specimen, the image being formed by using charged particles or electromagnetic waves emitted from the specimen irradiated with the charged particle beam;
a marker display unit for displaying a marker on each target position on an image of the specimen, the image being displayed on a viewscreen of the image display unit;
a marker position input unit for designating reference positions on the image of the specimen, on which respective markers are displayed; and
a marker position calculation unit for calculating the position on which each marker is displayed on the image of the specimen on the viewscreen of the image display unit;
wherein, when the specimen stage is moved, the position on the image of the specimen on which each marker is to be displayed is also moved based on both the calculated position of each marker, which has been calculated by the position calculation unit, and on the amount of displacement of the moved specimen stage, the amount of displacement being detected by the detector.
The present invention further provides a charged particle beam irradiation apparatus comprising:
a charged particle beam optical unit for irradiating a specimen with a charged particle beam;
a charged particle beam deflection unit for moving an area on the specimen, which is irradiated with a charged particle;
an image display unit for displaying an image of the specimen, the image being formed by using charged particles or electromagnetic waves emitted from the specimen irradiated with the charged particle beam;
a marker display unit for displaying a marker on each target position on the image of the specimen, the image being displayed on a viewscreen of the image display unit;
a marker position input unit for designating reference positions on the image of the specimen, in which respective markers are displayed; and
a marker position calculation unit for calculating the position on which each marker is displayed on the image of the specimen on the viewscreen of the image display unit, along with the amount of displacement of the image moved by the charged particle beam deflection unit;
wherein, when the image is moved by the charged particle beam deflection unit, the position on the image of the specimen on which each marker is to be displayed is also moved, based on both the calculated position of each marker, the position being calculated by the position calculation unit, and the amount of displacement of the image, the image displacement being calculated by the position calculation unit.
Moreover, in accordance with the above charged particle beam irradiation apparatus, the marker display unit displays a marker on the position on the image of the specimen corresponding to the same position in the coordinate system for the specimen, even if the image of the specimen is moved by moving the specimen stage.
Further, in accordance with the above charged particle beam irradiation apparatus, the marker display unit automatically displays markers by successively changing each of subindices for the markersxe2x80x94each marker being labeled with a subindex including a letter and/or a numeralxe2x80x94on positions where the marker position calculation unit determines that markers should be displayed, based on subindices input for markers attached to at least two reference positions on the image of the specimen, the reference positions being designated from the marker position input unit.
Also, in accordance with the above charged particle beam irradiation apparatus, when one of the subindices is selected, the marker display unit moves the image of the specimen so that a marker labeled with the selected subindex is displayed on the viewscreen of the image display unit.
Additionally, in the above charged particle beam irradiation apparatus, the marker display unit displays markers on positions on the image of the specimen, determined based on the direction and a pitch between two neighboring positions calculated by using a first reference position and a second reference position on the image of the specimen, the two reference positions being input from the marker position input unit.
On top of that, in accordance with the above charged particle beam irradiation apparatus, the marker display unit displays markers on positions on the image of the specimen, obtained by dividing the interval between the first and second reference positions on the image of the specimen by an input division number, the two reference positions being input from the marker position input unit.
Furthermore, the present invention provides a method of irradiating a specimen with a charged particle beam and displaying an image of the specimen, the image being formed by using charged particles or electromagnetic waves emitted from the specimen irradiated with the charged particle beam, the method comprising the steps of:
displaying a marker on each target position on an image of the specimen, the image being displayed on a viewscreen of the image display unit;
reading in and calculating the position of the displayed image on which the marker is displayed, in the coordinate system for the viewscreen;
moving a specimen stage on which the specimen is held
detecting the amount of displacement of the moved specimen stage; and
moving the marker to a new position to be located in the coordinate system for the viewscreen based on both the read-in and calculated position and the detected amount of displacement of the moved specimen stage.
Moreover, the present invention also provides a method of irradiating a specimen with a charged particle beam and displaying an image of the specimen, the image being formed by using charged particles or electromagnetic waves emitted from the specimen irradiated with the charged particle beam, the method comprising the steps of:
displaying a marker on each target position on an image of the specimen, the image being displayed on a viewscreen of the image display unit;
reading in and calculating the position of the displayed image on which the marker is displayed, in the coordinate system for the viewscreen;
moving an irradiation region of the specimen, which is irradiated with a charged particle beam;
calculating the amount of displacement of the image of the specimen due to the moving of the irradiation region; and
moving the marker to a new position to be located in the coordinate system for the viewscreen based on both the read-in and calculated position and the calculated amount of displacement of the moved image.
By the above-mentioned marker display function according to the present invention, the marker displayed on the designated position in the specimen behaves as if the marker were adhered to the specimen. For example, in the charged particle beam irradiation apparatus according to the present invention, if the position on the image of the specimen, on which the marker is displayed, moves to the outside of the viewscreen, the marker also moves to the outside of the viewscreen along with the position on the image of the specimen, and disappears from the viewscreen. Conversely, if the position on the image of the specimen, on which the marker is to be displayed, moves into the viewscreen of the image display unit, the marker also moves into the viewscreen along with the above position on the image of the specimen, and is displayed on the viewscreen.
Furthermore, the charged particle beam irradiation apparatus and method according to the present invention has an ability to display a marker on each position on the image of the specimen, satisfying the direction and a pitch which are determined based on the positional relationship between designated first and second reference positions to which markers are attached, respectively, and an ability to display a marker on each of the positions on the image of the specimen, the positions being obtained by dividing the interval between the first and second positions on which markers are displayed, by a divisional number input from the input unit, and so on.
Further still, the charged particle beam irradiation apparatus and method according to the present invention has an ability to successively label each of the target positions to be observed on the image of the specimen with a subindex composed of a letter and/or a numeral by automatically changing the subindex. If the subindices are numerals, the markers are automatically labeled with subindices in an increasing order, such as a series of 1, 2, 3 . . . , or in a decreasing order, such as a series of 1, 3, 5, 7 . . . . On the other hand, if they are alphabetic letters, the markers are labeled with letters of a series of a, b, c . . . , or a series of z, y, x . . . . If the subindices are alphanumeric pairs, the markers are systematically labeled with subindices composed of the pairs by automatically changing the numerals in the subindices in an increasing or decreasing order.
If the markers are labeled with subindices, it is possible to provide an additional function for the charged particle irradiation apparatus, such that by inputting a marker with a subindex, an image of the specimen with the marker with the designated subindex is moved so as to be displayed on the viewscreen of the image display device.
The moving of the image of the specimen can be carried out by moving the specimen stage with the specimen stage drive unit or by moving an irradiation area of the specimen, which is two-dimensionally irradiated with a charged particle beam by the charged particle beam deflection unit.
Furthermore, the displaying of a marker with a designated subindex on the viewscreen of the image display device can be realized by adding a function to the charged particle beam irradiation apparatus, which calculates the necessary amount of movement of the irradiation area based on the present position of the marker with the designated subindex in the coordinate system for the viewscreen, and if the calculated amount of the movement of the irradiation position is within the range in which the irradiation area can be moved by the beam deflection unit, it moves the irradiation area by the calculated amount by using the charged particle beam deflection unit. Otherwise, the displaying of a marker with a designated subindex on the viewscreen can be realized by providing an additional function to control the specimen stage drive circuit so as to move the position of the marker with the designated subindex by the calculated amount.
According to the above function for moving the position of an image of a cell to which a designated marker is attached, it is possible to immediately return back the position of an image of a cell, on which the designated marker is to be displayed but which is outside the viewscreen, onto the viewscreen when a subindex in the target marker is input. Furthermore, markers can be automatically attached to the required positions on the image of the specimen by designating the first and second reference positions with two markers, respectively.
Also, a marker is attached to the position of an image of a desired cell in the specimen and displayed on the viewscreen, by moving a pointer controlled by a pointing device to the desired position and pushing a button switch of the pointer device at the position indicated by the pointer.
In accordance with the present invention, once an operator designates the position of an image of a cell in a specimen, which the operator intends to observe, by using a pointing device which controls a pointer such as a cross or arrow cursor, and attaching a marker with a subindex of a numeral and/or a letter to a desired position designated with the pointer, the attached marker can move along with the position to which the marker is attached when the specimen is moved. Accordingly, if the position on the image of the specimen to which a marker is attached leaves the viewscreen of the image display device, the marker also leaves the viewscreen. Conversely, if the position on the image of the specimen which has been outside the viewscreen returns to the viewscreen of the image display device, the marker is also displayed on the viewscreen. Thus, since a desired position on the image of the specimen can be found by searching or designating a marker attached to the desired position, and it is not necessary to memorize the position, the locating of the desired position can be efficiently performed by an operator. Moreover, if an operator designates two or more reference positions on the image of the specimen by attaching different markers to the respective reference positions, markers can be automatically attached to a plurality of positions on an image of the specimen. Furthermore, each marker can move along with a corresponding one of the plurality of positions to which the markers are attached. Thus, a field to be displayed on the viewscreen on the image of the specimen can be efficiently set even though the specimen is a semiconductor memory in which a number of unit cells are arranged in an orderly manner. In addition, if a subindex of a numeral and/or a letter is included in each marker, the efficiency of setting the displayed view field on the image of the specimen can be further improved.